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quantum mechanics, the multiverse, and "Dark Matter" (the novel)

So I'm stewing over two questions as a result of the scenes at the end of the Blake Crouch novel Dark Matter.

1. When there is a "decision point", the proverbial fork in the road, is a new universe created, at that instant, out of nothing, or did the alternate universe exist all along and was simply indistinguishable until the particular fork in the road differentiated them?

1a. Okay, 3 questions: If it's the former and not the latter, don't we have a problem with creating matter out of nothing?

2. When there is a "decision point", is probability a factor, or is the mere possibility of an outcome enough to create an instance of that outcome? Let's say you're at an intersection and the odds of Outcome-A are twice that of Outcome-B. Does that mean that Outcome-A must have happened twice for Outcome-B to have happened once? Do we now have 3 alternate universes instead of 2, but where two of them are indistinguishable (at least until another decision point causes them to diverge)?

Finally, I have a basic problem with the multiverse theory that has nothing to do with this particular novel, inasmuch as it proposes infinite alternate universes. If each "decision point" spawns a universe for each possible outcome, that would still be a finite number. While the eventual number of parallel universes would be so vast as to be uncountable, it could never be infinite. As an example, there couldn't be an alternate universe where I'm sitting here typing this, and everything is precisely the same except that I'm wearing a Taylor Swift tee-shirt, because if I were wearing a Taylor Swift tee-shirt, something else would also have to be different.

Do you want to discuss quantum mechanics as described in the book, or actual quantum mechanics? Although I have not read the book, I gather from your question that the author must have misunderstood at least one important aspect of quantum mechanics ("decision point").

The Many-Worlds interpretation is very unclear, when the universes diverge. Postulating a "decision point" is naive, only works in very simple cases, and reeks of backdoor Copenhagen. So, the universes being instantly created is certainly not true, but you could either gradually create universes, or have an infinite supply of universes at the the beginning. In both cases, there is no formal problem with creating matter out of nothing, because the rule for that only exists in-universe. Different rules for the meta-universe are unproblematic, since it was invented for this and is unconstrained by anything else. Of course, there are plenty of philosophical problems with all these universes ex nihilo.

There is also no clear answer for your second question, because you could postulate two universes with different probability weighting, or n*3 universes which are all equally likely. either way works. David Deutsch argued for the latter and I would say it is the cleaner option.

As for how many there are: Usually, the position of a particle is described in a continuous space with infinitely many possible positions. So even a single particle would spawn an infinite number of universe. You can argue that at one point we have to quantize spacetime, but then we do not know how exactly to do that (problems with General Relativity), so I would settle for "practically infinite". In physics, "infinite" does not actually mean "infinite", but "a number too big to care about its value", which this number certainly is.

The term "decision point" is mine. I don't want to talk too specifically about the book, beyond what a person can read in a review, but the author writes about "superposition" and the observer effect. I was just reaching for a term to describe the moment at which one universe splits into one or more universes. It's an idea that has appeared in science fiction for, I dunno, decades now (I'm thinking of "Mirror, Mirror" from the original Star Trek, '67 or '68). It's entirely possible that one can't really talk about the science of it and the science-fiction of it simultaneously, that they run in totally different directions. If so, since this is the Science & Technology forum and I don't want to spoil the book, let's stick with the science. Anyway, the science is where my head starts to hurt; I'm pretty good with the science-fiction.

And yeah, if physicists mean "a number too big to care about its value", then it makes a little more sense to me.

[...] but the author writes about "superposition" and the observer effect. I was just reaching for a term to describe the moment at which one universe splits into one or more universes.

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The observer effect only occurs in the context of the Copenhagen interpretation. Here, the observer makes a measurement, the wavefunction collapses and exactly one reality - or universe - emerges. The Many-Worlds interpretation tried to get rid of observers and measurements by including all observers into the quantum system, resulting in a global wavefunction and multiple realities. Unfortunately, it was not really successful in solving the measurement problem, because the question "When does the measurement occur?" has simply been replaced by the equivalent problem "When do the realities split?". Therefore, nobody knows when that moment you speak of occurs, or if it is even a moment and not a process during which the realities are partially split. Nevertheless, the term "observer effect" and is incompatible with multiple realities, because the latter where constructed to eliminate the former.

It's entirely possible that one can't really talk about the science of it and the science-fiction of it simultaneously, that they run in totally different directions.

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At some point that is usually the case with any science fiction story, because science fiction needs to tell a story and has to sacrifice scientific accuracy (If it were fully scientifically accurate, it would not be science-fiction any more, because it would have to mirror current - and not future - science). This is especially true for quantum mechanics, because although the effects are amazing on the microscopic level, the macroscopic results are usually not that spectacular.

Anyway, the science is where my head starts to hurt;

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That is normal. If the head does not hurt at least a little bit, you are not thinking hard enough about it.

Nevertheless, the term "observer effect" and is incompatible with multiple realities, because the latter where constructed to eliminate the former.

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Right, most science fiction vaults right over that, goes ahead and establishes that there is an alternate universe (or many) and concentrates on how one might travel from one to the other in order to see the differences. Dark Matter tries to actually address the observer effect problem, but of course it does it in a sci-fi way, with a bit of hand-waving and theory-crafting, and then just dives into the story. The author references Schrodinger's Cat a few times, too, which is an idea that I've always felt I'm not quite getting my head around, no matter how many times I read up on it.

The author references Schrodinger's Cat a few times, too, which is an idea that I've always felt I'm not quite getting my head around, no matter how many times I read up on it.

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The funny thing is: You are not supposed to. The example was constructed by Schrödingerto point out the absurdity of quantum mechanics. He sort of lost the argument there, but the example remained. It is not very useful at anything, because it is too complicated to explain quantum mechanics with it and it is too far from reality to test anything with it (it is too hard to build a cat-sized box that you cannot look into). So it has become something of a buzzword and the quantum physics community (which tends to be quite buzzword-centered these days) has unfortunately picked up on that and made Schrödinger's-cat states a scientific term.

Right, most science fiction vaults right over that, goes ahead and establishes that there is an alternate universe (or many) and concentrates on how one might travel from one to the other in order to see the differences.

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It is interesting though to speculate if we could actually access the parallel universes from the many worlds-interpretation. You'd need to introduce a term in the Schrödinger equation that acts on the wave function squared. That makes little sense within standard quantum mechanics because the wave function amplitude is arbitrary. You would get wave function phase and amplitude as new observable quantities, and the biggest effects might be visible at the point where all history converges and the wave function amplitude is large.

It is interesting though to speculate if we could actually access the parallel universes from the many worlds-interpretation.

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I would argue, it is impossible by definition. To access other universes you would have to introduce an effective interaction between them. But according to the MWI, branches of the wavefunction represent different universes as soon as there is no effective interaction between them. So if we could access another universe, it would not be another universe.

I guess your argument will result in something similar. If you start adding terms to the equations of quantum mechanics, you end up with different physics. As the MWI is specifically for quantum mechanics, it might not apply to the new physics. The new system might have very different interpretations. So you could lose the reason for multiple worlds by setting up a mechanism to access them.

I guess your argument will result in something similar. If you start adding terms to the equations of quantum mechanics, you end up with different physics. As the MWI is specifically for quantum mechanics, it might not apply to the new physics. The new system might have very different interpretations. So you could lose the reason for multiple worlds by setting up a mechanism to access them.

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In some sense, yes and no. Because usual quantum mechanics would still apply in the limiting case. Having such an additional term which is just too weak to notice with current instruments is not entirely unprecedented.

I am wondering about a tied matter:
In an experiment setting, you have to have observers and any input is (regardless of type of getting the input) inherently tied to the observer's means of picking it up/sensing/thinking and so on. While one can theorize on what the state itself is without any observer, that notion is a singular point (it cannot be further examined; it is a "thing in itself", ie it is 'what would be identified if we don't identify or pick it up' or the alternative and problematic idea of 'what a being with infinite means of examining it would pick up").
So i am not seeing how this barrier is suited in the world of physics or other sciences dependent on experiments, cause they are inherently tied to our senses of phenomena.

I am wondering about a tied matter:
In an experiment setting, you have to have observers and any input is (regardless of type of getting the input) inherently tied to the observer's means of picking it up/sensing/thinking and so on. While one can theorize on what the state itself is without any observer, that notion is a singular point (it cannot be further examined; it is a "thing in itself", ie it is 'what would be identified if we don't identify or pick it up' or the alternative and problematic idea of 'what a being with infinite means of examining it would pick up").

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That is subject to interpretation. The Many Worlds interpretation does postulate an absolute reality that a being external to the universe could pick up, it is just that we are getting stuck on an ever dwindling branch of that reality. But in the other mainstream interpretations, the outcome of a (non-commuting) measurement that has not been performed cannot be known.

So i am not seeing how this barrier is suited in the world of physics or other sciences dependent on experiments, cause they are inherently tied to our senses of phenomena.

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Science is only concerned with the things that could be measured. Any question regarding things that cannot ever be measured are inherently unscientific. So that barrier - if real - is the limit of science. That should not stop us from probing that barrier to see whether it is actually there.

But do beasts really exist, or do they just stand in for things which we do not understand well enough?

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I see it this way: even if nothing else is monstrous, we still obviously have the idea of that which is monstrous and thus it already exists in our mind.
Now whether or not it has to be tied to a barrier in our development of theories... i can't say. But even if the sea is miles away from the small number of houses, you'll still be next to it in a future expansion of the settlement to all sides. (well, if really akin to a sea you'll sink into it too if you dig deep enough).

At any rate that we can feel horror, and devise frightening thoughts, doesn't have to mean anything in regards to cosmic things. We may just be hitting upon more of our own walls, as usual.

Λέων μεν ὄνυξι κρατεῖ, κέρασι δε βούς, ἄνθρωπος δε νῷι
"While the lion prevails with its claws, and the ox through its horns, man does by his thinking"
Anaxagoras of Klazomenae, 5th century BC

It is logical extension of the quantum suicide idea, so if you buy into the many-worlds interpretation, it is not too crazy. But I have two objections:
The first is about the instantaneous part. If a local event causes a destruction of the universe, I would assume that destruction to be bounded by the speed of light. Otherwise you would get problems with causality as we understand it. That might cause us to be able to see it coming, even if it occurs at the speed of light. For example, we might notice the (lack of?) gravitational effects on the light that is reaching us just ahead of it*. You can get around that by saying that these events do not have to follow the usual rules of physics, because we have not observed and can never observe these, but this brings me to my second objection:

The idea requires the universe to be in some strange bistable state: Either everything is fine and we can observe physics as we know it, or the universe gets instantly destroyed. Why are there no events that are just below the universe-destroying threshold that take out half the universe or just a star? Why is faster-than-light transfer of information only possible when it destroys the universe? Obviously, such a mechanism is not entirely impossible, but it sounds quite improbable.

*That sounds like the beginning of a trashy movie: Scientists discover that the universe is collapsing and the hero and his/her sidekick have to rescue it with the power of love or something.